Amp Draw – How Much Do You Need

Living on battery power is going to be different for everyone and there is no consistency across coaches or even among coaches of similar brands and models. Even if we had the exact same brand and model of coach, our power requirements are going to be different. After all, you may not turn on the light when you go to the bathroom in the middle of the night or may leave the TV on whether you are watching it or not. What happens is that the same appliances and electrical devices will have the same power requirements but two people, living in a motorhome, do not have the same power requirements as the two people next door.

While these lithium ion batteries have worked for us just fine (it’s still very early in the testing), they may not work for you in the same manner. This is something you need to figure out.

Due to how much we have boondocked over the years—at this time we are into our ninth year of fulltiming—I have a really good “feel” for my power requirements. There are two ways you can go about figuring out what you need and they are…

Track it exactly… Every appliance, device, lightbulb, and anything electrical on your coach has an identifiable amp draw. Build a simple spreadsheet and note this. With complete information, you can know your exact power requirements at any given time. The sum of whatever electrical devices you are operating plus “phantom” draw can be calculated. The downside to this method is that you cannot compensate for momentary usage of some devices. For example, when putting out a slide you will require some battery power but that requirement is only for a few seconds—it is not an ongoing draw. However, if you turn on ceiling lights, those individual lights are drawing power (while on) but you also need to factor in the multiple (number of lights that are on).

Know Your Lifestyle… This is knowing what power requirements you have for certain “normal” behaviors in lifestyle. For example, I know (from several years in this coach) that when we stop in the afternoon with no other plans, the TV is usually not on, no lights are on, the computer and satellite controllers are always on, Sandy is typically reading, I am reading or working on the computer, and our fridge is opened maybe once per hour for something to drink or munch on. When we are living like this (and we do nearly every day), our power requirements range from 24–28 amps.

Phantom Amps
You will have virtually no control over what is called “phantom amps.” This is the amount of current needed to maintain various electrical “things” even though the appliance may be physically turned off. Many/most electronic devices continue to draw a bit of current all the time. For example, look at the clock on your microwave—it’s powered by something. This “phantom” current draw gives you the convenience of “instant on” and is different from the old “warm up” time needed for appliances years ago. Now, when you hit that “On” button, you expect immediate results. Monitoring devices in your coach will always draw current, too (otherwise they would stop monitoring). All this requires a bit of power (current) all the time. Therefore, the number of devices you have in your coach has a cumulative effect on the battery power and is always using current. That “effect” is called phantom amps.

I found it easiest to learn the amount of phantom-amp draw on my coach by turning off everything we normally use and getting ready to go to bed. I simply looked at my Aladdin to see what that draw was without us actually using anything. Whatever your phantom amp reading is, this will be an integral part of the total current you are using at any given time.

[Author Note… As I write this, we are parked in an Interstate Rest Area (obviously not hooked up to any utilities), planning to spend the night, it is 5:00 PM on a pleasant sunny afternoon, not ready to start preparing dinner just yet, and we are drawing about 23 amps. I have been watching this carefully. We have been using this amount since we parked and as I said earlier, this amp draw is very normal for us under these conditions.]

More Normal Lifestyle
About 6:30 PM, we started preparing dinner. At this time several things happen. The daylight will be fading and the front TV will be turned on (plus those related appliances—DVD, DVR, satellite controller). I will turn on several ceiling and under-cabinet lights in the kitchen (NEVER chop veggies in the dark with a sharp knife), if we need to thaw something from the freezer, we will run the generator for about 15 minutes, and continue to cook. We will then sit down to eat, the kitchen and under-cabinet lights will be turned off but table and dining ceiling lights will be turned on. During the dinner preparation and eating time, our power draw is about 60A.

By 8:30 PM, we are finished with the clean-up from dinner and settle in for some serious TV time. Only one light is on (over the stove) plus the front TV and related goodies are on. We do this until about 10:00 PM when Sandy goes to bed. During our TV time, our power draw is about 53A.

Around 10:00 PM, Sandy goes in back (to the bedroom) and turns on that TV (plus its DVR). There will be no additional lights on. I stay up until about 1:00 AM every night and will watch TV or read. Usually if I read, I turn off the front TV. During this time, our power draw is about 56A.

So What Does This Mean
It works like this… since I have a 400 amp-hour coach battery, I should be able to get the equivalent of 400 amps of current out of it (assuming it is fully charged). For example, if I was using 100 amps per hour, then I should be able to live off that battery for four hours. If I were using 50 amps per hour, then I should be able to live off that battery for 8 hours (400 / 50 = 8). But none of us uses or needs battery power (current) at a steady rate so we cannot guess at how long our battery will last. This is why you need a really good “feel” for your usage and the only way to determine (guess/estimate) how long you should be able to live off your battery power on each charge cycle.

Wrap Up
While I have described our “normal” lifestyle above, yours will be different. Plus, we never—repeat: NEVER—operate a single high-amp-draw appliance solely from the battery. No microwave, no coffeepot, no hair dryer, no toaster, no nothing. These will suck a battery down in a heartbeat.

For example, when Sandy gets up, she will start the generator, make the coffee, shut off the coffee-maker and the generator, and put the coffee-maker carafe on the stove (using a heat diffusion plate). The burner is on low but this keeps the coffee hotter than the coffeepot.

You need to have a “feel” for your battery usage, too, but there is no need to have this calculated down to the last 1/10th amp. Knowing your needs, understanding how you live and use the available current, and meeting your needs in terms of “staying longer” when boondocking will help you decide what size lithium ion battery you can use in your coach.

[Author Note… Contact me any time and check back here for the updates. Please, tell your friends, dealer, post to your RV forums and e-mail groups that they can get the unbiased info here at… aboutrving.com